Grass collection systems for lawn mowers fall into two categories: active and passive systems. Passive systems may rely on air currents generated by mowing blades to propel the cut grass into a bin, bag, or other catcher. Active systems may have an impeller or blower that propels the cut grass into a bin, bag, or other catcher.
Active grass collection systems are powered by the lawn mower and can create large amounts of vacuum force to collect the grass clippings as well as mechanical propulsion to speed the clippings to a collection bin. In many cases, active grass collection systems are effective even when the grass may be thick and wet. Active grass collection systems are often used on commercial mowers where large mowing decks may create large amounts of clippings.